This invention relates to electronic and hydraulic controls for determining the length of strokes of weights in hydraulic hammers, and particularly to controls for sensing different impact levels of weights for initiating uniform length of strokes above various impact levels.
The stroke control of this invention is particularly applicable to mobile hydraulic hammers similar to the one described in U.S. Pat. No. 3,384,186 issued on May 21, 1968 to D. E. Broderson et al for Mobile Hydraulic Hammer. These hammers raise heavy weights to controlled heights by operation of hydraulic cylinders and then let the weights fall on materials to be either impacted or broken. In a typical mobile hydraulic hammer, the weight is raised by a hydraulic cylinder; the expansion of the cylinder is controlled by operation of one or more hydraulic valves; and the operations of the valves are controlled by solenoids that are operated by electrical or electronic control circuits. The present invention is directed to improvement of the electronic control circuits.
As in U.S. Pat. No. 3,384,186 to which reference has been made above, the control circuit includes a timing circuit for determining the length of time that a hydraulic cylinder fills to determine the height of a hammer weight. In this particular reference, operation of one manual control determines the time for pumping fluid into the hydraulic cylinder, and operation of another control determines the period between the dropping of the hammer weight and the starting of a successive lift. When surface that is being compacted or broken is quite level, these controls can be set to provide a desired height to which the hammer weight is lifted and to determine that the lifting period will be started immediately upon impact. Controls on other equipment may sense a particular level through which a hammer passes to determine the starting of a succeeding stroke. Such a control is described in U.S. Pat. No. 3,938,595 issued to William J. Swenson on Feb. 17, 1976 for Apparatus and Method for Driving Bulb Piles.
In practice, mobile hydraulic hammers are often used to compact earth where the lowest level to which a hammer travels varies substantially. Manual controls that determine intervals of operation and do not compensate automatically for different levels of impacts must be adjusted constantly in an effort to approach the desired length of stroke and the maximum rate of operation, the maximum rate being achieved when each succeeding stroke is started immediately after impact. Manual adjustment of these controls is tedious, and even skilled operation of the controls cannot always provide either the desired length of stroke or the maximum rate of operation.